Recent advances in pressure-sensitive copying paper have led to its use in widely expanded fields. The pressure-sensitive copying paper itself has been improved to a large extent and a number of new dyes and color developing systems have been successively developed. In the prior art, PCB (polychlorinated biphenyl) was exclusively used as a solvent for dye used in the paper. However, recently the use of PCB has been prohibited because of its toxicity and recognition as a pollutant. Therefore, as a substitute for PCB various aromatic hydrocarbon solvents were developed. While the use of pressure-sensitive copying paper has recently expanded into various fields and color systems are more effectively developed, these aromatic hydrocarbon solvents are found not to provide a sufficient rate of color development of the dye.